The invention relates to a power semiconductor device, and in particular, to suppression of surge occurring in the power semiconductor device.
Power semiconductor devices including power semiconductors are used widely. A power module is a package incorporating a plurality of power semiconductor elements such as metal oxide semiconductor field effect transistors (MOSFET) or insulated gate bipolar transistors (IGBT) with peripheral circuits therefor. Its advantages are its compact size due to the integration and easy wiring. Thus, power modules are used in many purposes.
It is required for a power semiconductor device to prevent a bad influence due to surge. For example, a driver for power semiconductor elements in an inverter circuit, disclosed in Japanese Patent laid open Publication No. 7-297695/1995, includes a protection circuit for preventing overheating. Such a protection circuit may malfunction due to a sharp current change on reverse recovery of a flywheel diode provided for the power semiconductor element. Then, in order to prevent such a malfunction, a controller, having a common output terminal for sending an alarm signal when a surge current or a short-circuit current happens, connects a Schottky diode between a common output terminal of a controller for a lower arm and a power source terminal, so that a current flowing in a reverse direction is prevented in a circuit board of the controller. Alternatively, a capacitor is connected between the common output terminal of the controller circuit and the ground terminal, to prevent fluctuations of the reference voltage in the circuit board of the controller.
When a power semiconductor device is used, a peripheral circuit such as a gate driver or a photo-coupler, or an external signal generator such as a microprocessor for supplying a control signal to a gate driver may be broken due to surge current or voltage generated in the power semiconductor device. However, for example, the above-mentioned inverter cannot block the surge voltage or current, or cannot prevent the bad influence to a device connected to the power semiconductor device. Then, a surge voltage in the inverter circuit may be applied to or a surge current in the inverter circuit may flow to a peripheral device, and in such a case the peripheral device may be broken, or an electric loss increases.